Anisotropic conjugated polymer chain conformation tailors the energy migration in nanofibers

Conjugated polymers are complex multi-chromophore systems, with emission properties strongly dependent on the electronic energy transfer through active sub-units. Although the packing of the conjugated chains in the solid state is known to be a key factor to tailor the electronic energy transfer and the resulting optical properties, most of the current solution-based processing methods do not allow for effectively controlling the molecular order, thus making the full unveiling of energy transfer mechanisms very complex. Here we report on conjugated polymer fibers with tailored internal molecular order, leading to a significant enhancement of the emission quantum yield. Steady state and femtosecond time-resolved polarized spectroscopies evidence that excitation is directed toward those chromophores oriented along the fiber axis, on a typical timescale of picoseconds. These aligned and more extended chromophores, resulting from the high stretching rate and electric field applied during the fiber spinning process, lead to improved emission properties. Conjugated polymer fibers are relevant to develop optoelectronic plastic devices with enhanced and anisotropic properties.Comment: 43 pages, 15 figures, 1 table in Journal of the American Chemical Society, (2016

Comparative Raman Study of Organic-Free and Surfactant-Capped Rod-Shaped Anatase TiO2 Nanocrystals

Excitation of lattice vibrations in nanostructured anatase TiO2 frequently occurs at energy values differing from that found for the corresponding bulk phase. Particularly, investigations have long aimed at establishing a correlation between the low-frequency E-g(1) mode and the mean crystallite size on the basis of phonon-confinement models. Here, we report a detailed Raman study, supported by X-ray diffraction analyses, on anatase TiO2 nanocrystals with rod-shaped morphology and variable geometric parameters, prepared by colloidal wet-chemical routes. By examining the anomalous shifts of the E-g(1) mode in the spectra of surfactant-capped nanorods and in those of corresponding organic-free derivatives (obtained by a suitable thermal oxidative treatment), an insight into the impact of exposed facets and of the coherent crystalline domain size on Raman-active lattice vibrational modes has been gained. Our investigation offers a ground for clarifying the current lack of consensus as to the applicability of phonon-confinement models for drawing information on the size of surface-functionalized TiO2 nanocrystals upon analysis of their Raman features

An Insight into Chemistry and Structure of Colloidal 2D-WS2 Nanoflakes: Combined XPS and XRD Study

The surface and structural characterization techniques of three atom-thick bi-dimensional 2D-WS2 colloidal nanocrystals cross the limit of bulk investigation, offering the possibility of simultaneous phase identification, structural-to-morphological evaluation, and surface chemical description. In the present study, we report a rational understanding based on X-ray photoelectron spectroscopy (XPS) and structural inspection of two kinds of dimensionally controllable 2D-WS2 colloidal nanoflakes (NFLs) generated with a surfactant assisted non-hydrolytic route. The qualitative and quantitative determination of 1T’ and 2H phases based on W 4f XPS signal components, together with the presence of two kinds of sulfur ions, S22− and S2−, based on S 2p signal and related to the formation of WS2 and WOxSy in a mixed oxygen-sulfur environment, are carefully reported and discussed for both nanocrystals breeds. The XPS results are used as an input for detailed X-ray Diffraction (XRD) analysis allowing for a clear discrimination of NFLs crystal habit, and an estimation of the exact number of atomic monolayers composing the 2D-WS2 nanocrystalline samples

Assembled Nanostructured Architectures Studied By Grazing Incidence X-Ray Scattering

In this chapter, we will focus on a specific X‐ray-based technique among those employed in surface science and which is especially suitable for the study of self‐assembled nanocrystals: Grazing Incidence Small Angle X‐ray Scattering (GISAXS). We will first introduce the main field of investigation considered herein, with basic notions of X‐ray scattering from surfaces, and then address basic concepts about GISAXS. Finally, we will describe a few relevant examples of studies, of nanostructured architectures, through ex situ and in situ experiments of grazing incidence X‐ray scattering. This manuscript is focused on the former, showing that they can be performed by using laboratory instruments. In situ investigations still need synchrotron radiation sources in most cases; therefore, only a few examples selected from the literature are reported here, for the sake of completeness. The experiments described are mainly performed in the small angle range, providing information on the size and shape of nanocrystals, together with their spatial arrangement. Both 2D and 3D architectures are considered. In particular, GISAXS measurements of 2D superlattices of nano‐octapods, performed both at a third generation synchrotron beamline and with a table‐top set‐up, are compared; the employed table‐top set‐up is described in a dedicated paragraph. Further examples of grazing incidence studies as performed by the authors with a table‐top set‐up are reported: a GISAXS study of 3D iron oxide nanocrystal superlattices, showing the importance of modelling in order to obtain structural information from data; a combined small/wide angle scattering (GISAXS/GIWAXS) study of 3D PbS nanocrystal superlattices; and a GIWAXS study of P3HT nanofibres, showing how the ordering at the molecular and atomic length scales can be obtained by exploring different angular ranges in the same grazing incidence geometry. Finally, selected examples of in situ GISAXS studies, performed with synchrotron radiation sources, are described

Solvothermal Synthesis, Gas-Sensing Properties, and Solar Cell-Aided Investigation of TiO2-MoOx Nanocrystals

Titania anatase nanocrystals were prepared by sol-gel/solvothermal synthesis in oleic acid at 250 °C, and modified by co-reaction with Mo chloroalkoxide, aimed at investigating the effects on gas-sensing properties induced by tailored nanocrystals surface modification with ultra-thin layers of MoO species. For the lowest Mo concentration, only anatase nanocrystals were obtained, surface modified by a disordered ultra-thin layer of mainly octahedral Mo oxide species. For larger Mo concentrations, early MoO phase segregation occurred. Upon heat treatment up to 500 °C, the sample with the lowest Mo concentration did not feature any Mo oxide phase segregation, and the surface Mo layer was converted to dense octahedral Mo oxide. At larger Mo concentrations all segregated MoO was converted to MoO. The two different materials typologies, depending on the Mo concentration, were used for processing gas-sensing devices and tested toward acetone and carbon monoxide, which gave a greatly enhanced response, for all Mo concentrations, to acetone (two orders of magnitude) and carbon monoxide with respect to pure TiO. For the lowest Mo concentration, dye-sensitized solar cells were also prepared to investigate the influence of anatase surface modification on the electrical transport properties, which showed that the charge transport mainly occurred in the ultra-thin MoO surface layer

In-plane Aligned Colloidal 2D WS2 Nanoflakes for Solution- Processable Thin Films with High Planar Conductivity

Two-dimensional transition-metal dichalcolgenides (2D-TMDs) are among the most intriguing materials for next-generation electronic and optoelectronic devices. Albeit still at the embryonic stage, building thin films by manipulating and stacking preformed 2D nanosheets is now emerging as a practical and cost-effective bottom-up paradigm to obtain excellent electrical properties over large areas. Herein, we exploit the ultrathin morphology and outstanding solution stability of 2D WS2 colloidal nanocrystals to make thin films of TMDs assembled on a millimetre scale by a layer-by-layer deposition approach. We found that a room-temperature surface treatment with a superacid, performed with the precise scope of removing the native insulating surfactants, promotes in-plane assembly of the colloidal WS2 nanoflakes into stacks parallel to the substrate, along with healing of sulphur vacancies in the lattice that are detrimental to electrical conductivity. The as-obtained 2D WS2 thin films, characterized by a smooth and compact morphology, feature a high planar conductivity of up to 1 μS, comparable to the values reported for epitaxially grown WS2 monolayers, and enable photocurrent generation upon light irradiation over a wide range of visible to near-infrared frequencie

Inorganic photocatalytic enhancement : Activated RhB Photodegradation by surface modification of SnO2 Nanocrystals with V2 O5-like species

Ajuts: CSIC/CNR project 2010IT0001 (SYNCAMON), SOLAR project DM19447, VINNOVA Marie Curie Incoming Grant under "Light Energy" project.SnO nanocrystals were prepared by precipitation in dodecylamine at 100 °C, then they were reacted with vanadium chloromethoxide in oleic acid at 250 °C. The resulting materials were heat-treated at various temperatures up to 650 °C for thermal stabilization, chemical purification and for studying the overall structural transformations. From the crossed use of various characterization techniques, it emerged that the as-prepared materials were constituted by cassiterite SnO nanocrystals with a surface modified by isolated V(IV) oxide species. After heat-treatment at 400 °C, the SnO nanocrystals were wrapped by layers composed of vanadium oxide (IV-V mixed oxidation state) and carbon residuals. After heating at 500 °C, only SnO cassiterite nanocrystals were obtained, with a mean size of 2.8 nm and wrapped by only V O-like species. The samples heat-treated at 500 °C were tested as RhB photodegradation catalysts. At 10 M concentration, all RhB was degraded within 1 h of reaction, at a much faster rate than all pure SnO materials reported until now

Evidence of Unprecedented High Electronic Conductivity in Mammalian Pigment Based Eumelanin Thin Films After Thermal Annealing in Vacuum

Melanin denotes a variety of mammalian pigments, including the dark electrically conductive eumelanin and the reddish, sulfur-containing, pheomelanin. Organic (bio)electronics is showing increasing interests in eumelanin exploitation, e.g., for bio-interfaces, but the low conductivity of the material is limiting the development of eumelanin-based devices. Here, for the first time, we report an abrupt increase of the eumelanin electrical conductivity, revealing the highest value presented to date of 318 S/cm. This result, obtained via simple thermal annealing in vacuum of the material, designed on the base of the knowledge of the eumelanin chemical properties, also discloses the actual electronic nature of this material's conduction

Silicon photomultipliers: On ground characterizations and modelling for use in front-end electronics aimed to space-borne experiments

Abstract Silicon Photomultipliers (Si-PM) consist of an array of semiconductor photodiodes joint on the common substrate and operating in limited geiger mode. A new generation of Si-PM is currently under test in INFN Rome Tor Vergata facilities: they consist of a 5625 element, 3 * 3 mm 2 array with an improved light response. These elements have been characterized. Furthermore, a functional model of the Si-PM has been developed to be used in a VLSI development of front-end electronics

Transferrin receptor 2 controls bone mass and pathological bone formation via BMP and Wnt signalling

Transferrin receptor 2 (Tfr2) is mainly expressed in the liver and controls iron homeostasis. Here, we identify Tfr2 as a regulator of bone homeostasis that inhibits bone formation. Mice lacking Tfr2 display increased bone mass and mineralization independent of iron homeostasis and hepatic Tfr2. Bone marrow transplantation experiments and studies of cell-specific Tfr2 knockout mice demonstrate that Tfr2 impairs BMP-p38MAPK signaling and decreases expression of the Wnt inhibitor sclerostin specifically in osteoblasts. Reactivation of MAPK or overexpression of sclerostin rescues skeletal abnormalities in Tfr2 knockout mice. We further show that the extracellular domain of Tfr2 binds BMPs and inhibits BMP-2-induced heterotopic ossification by acting as a decoy receptor. These data indicate that Tfr2 limits bone formation by modulating BMP signaling, possibly through direct interaction with BMP either as a receptor or as a co-receptor in a complex with other BMP receptors. Finally, the Tfr2 extracellular domain may be effective in the treatment of conditions associated with pathological bone formation